Add support for hints

[willemolding]

The Cannon-vm supports hints as an optional way for the guest program to communicate with the host. It has no effect in the on-chain VM.

This is used in Optimism for example to allow the guest to advise the host to pre-fetch certain pieces of chain data early in execution rather than when it is needed via the pre-image oracle.

Cannon-rs currently does not support the hint syscalls and these should be added for full support.